(a) Field of the Invention
The present invention relates to an internal combustion engine. More particularly, the present invention relates to a method and apparatus for controlling an electronic variable valve apparatus of an internal combustion engine.
(b) Description of the Related Art
Performance of an internal combustion engine, especially a gasoline engine, substantially depends on how efficiently an air can be drawn into a combustion chamber.
For better intake efficiency, a variable valve apparatus for varying valve timing is employed such that optimal amount of air can be drawn into the combustion chamber for various engine speeds.
A hydraulic variable valve apparatus that is typically employed has a drawback in that, when the engine speed is low or engine oil is at a low temperature, a torque for operating the apparatus is increased. In addition, such a hydraulic variable valve apparatus does not usually provide sufficient variation of cam angle.
In order to solve such drawbacks, an electronic variable valve apparatus is widely studied as an alternative for such a hydraulic variable valve apparatus.
The electronic variable valve apparatus shows many merits. For example, it shows higher response speed that a conventional hydraulic variable valve apparatus. An oil pump of an engine may be downsized since the electronic variable valve apparatus does not require a hydraulic pressure. The electronic variable valve apparatus can be properly operated even if the engine speed is low or the engine oil is at a low temperature, which means that a load for starting the engine may be reduced. Furthermore, an exhaust gas may be reduced when the engine is at a low temperature.
In addition the electronic variable valve apparatus may be operated at a wider range of an angle, such that the merits of varying the valve timing may be maximized.
The electronic variable valve apparatus are typically driven by an electronic clutch or a motor.
The scheme employing the electronic clutch costs less but it is harder to control. The scheme employing the motor cost more but it is easier to control.
An example of the electronic variable valve apparatus can be found in Japanese Patent Laid-Open Publication No. 2002-276310.
In order to control an angle of a camshaft according to the conventional scheme, an engine control unit calculates an angular difference Δθ between a reference angle depending on an engine state and a current angle detected by a cam angle sensor, and determines whether the angular difference Δθ is above a predetermined error value.
When the angular difference Δθ is less than the predetermined error value, the current control is maintained, and a clutch release coil and a brake control coil is not applied with a current.
When the angular difference Δθ is above the predetermined error value, it is determined whether the angular difference Δθ is positive or negative. If the angular difference Δθ is positive, a current is applied to the clutch release coil and the brake control coil so as to perform an advance control. If the angular difference Δθ is negative, a current is applied to the clutch release coil and the brake control coil so as to perform a retardation control.
According to the above scheme where a current to be applied to the clutch release coil and the brake control coil is on/off controlled in order to control an angle of a camshaft, calibration maps should be provided depending on control responsiveness, angular error, and engine states.
According to such a scheme, huge amount of experimentation is required in order to prepare sufficiently precise calibration maps, which causes the cost for newly designing a vehicle to increase very high.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.